Structured heavy duty liquid (HDL) detergent compositions are attracting more and more attention. First, structured HDL detergent compositions typically have higher viscosity than unstructured compositions at room temperature and under ambient pressure. Such higher viscosities are perceived by some consumers as containing more cleaning surfactants, being more concentrated, or of better quality. It is therefore desirable to provide structured HDL compositions to better delight consumers. Further, such structured HDL may suspend water-immiscible materials or water-insoluble particles, such as perfume, silicone fluid, mica, or titanium dioxide particles. Such water-immiscible materials or water-insoluble particles can impart various functional, sensory or aesthetic benefits to the HDL detergent compositions. However, such materials and particles tend to phase separate or precipitate out of the HDL detergent compositions when the compositions are exposed to heat, pressure, or agitation—during transportation or extended storage. HDL detergent compositions that have phase separated or contain visible precipitates are perceived by the consumers as being messy, expired, or of poor quality. It is therefore desirable to provide structured HDL detergent compositions that can suspend water-immiscible materials or water-insoluble particles but without undergoing phase separation or precipitation during transportation or extended storage.
It has been reported to use external structurants in HDL detergent compositions to help form structured phase and suspend water-immiscible or water-insoluble ingredients. One such external structurant is hydrogenated castor oil (HCO), which has a thread-like, crystalline structure. However, a separate premix unit is often needed to enable incorporation of HCO into HDL detergent compositions, resulting in additional capital investment and manufacturing cost. In addition, since the HDL detergent compositions need to be pumped through pipelines under high shear conditions during the manufacturing process, it is desirable that such liquid detergent compositions remain stable (i.e., without undergoing phase separation) at high shear. However, a HDL composition containing HCO is often very sensitive to high shear, e.g., it may phase separate when exposed to high shear inside the manufacturing pipelines, which brings challenges to the manufacturing process design. Another drawback for HDL products containing external structurants such as HCO is that these HDL products usually have a non-homogenous appearance, due to the phase separation of HCO, which may negatively impact the consumer's visual perception of the products and signal to the consumers that the product is of relatively lower quality.
Thus, there is a need for a stable, structured HDL detergent composition that minimized or is free of external structurant that may phase separate under high shear conditions. Preferably, such HDL detergent composition can be readily made by a simple batch-mixing process, without the need for a separate pre-mix unit for incorporating external structurants.
WO2014/113559 discloses a liquid detergent composition comprising from 5% to 20% by weight thereof of a surfactant system, which can function as an internal structurant to form a self-structured phase. Liquid detergent compositions disclosed by this reference are characterized by a pouring viscosity of from 2500 mPa·s to 6000 mPa·s at 20° C. and a ratio of medium shear viscosity to high shear viscosity of from 2 to 1. According to WO2014/113559, it is important that such liquid detergent compositions have relatively consistent viscosities at different shear rates, e.g., the viscosity decrease should not be more than half when the shear rate increases from as low as 0.01 s−1 to as high as 10 s−1. In other words, the liquid detergent compositions disclosed by WO2014/113559 have little or no shear thinning property, i.e., they could not become visibly “thinner” (i.e., there is no significant decrease in their viscosity) when they are exposed to higher shear rates.
However, for a structured HDL detergent composition, it is also desirable to have good shear-thinning property. On one hand, the HDL detergent composition should have a sufficiently high viscosity at a low shear rate, e.g., when it is placed in a stand-still position or under a slow pouring condition, in order to effectively suspend water-immiscible materials or water-insoluble particles. On the other hand, it is beneficiary for the viscosity of the HDL detergent composition to dramatically decrease when it is exposed to a significantly high shear rate, e.g., when the composition is pumped through manufacturing pipelines under high pressure. In this manner, the liquid detergent composition, which is now of a much lower viscosity and therefore much “thinner,” can flow easily through the pipelines during manufacturing, with minimal energy consumption.
Accordingly, there is also a need to provide an improved liquid detergent composition with good shear thinning property, which is characterized by a high viscosity at a lower shear rate and a significantly reduced viscosity at a higher shear rate.